Surgical staples and ligating clips are beginning to come into wide use in the surgical profession as an alternative to sutures and ligatures. One advantage of clips and staples in comparison with sutures and ligatures is that tissue fastening or ligating with a staple or clip, whether applied singly or as an array applied in a row or in a ring, is much simpler and faster than with a suture or a ligature. Surgical procedures can be speeded up, thereby reducing the length of time the patient must be anesthetized and shortening the operating room time. Thus, there are both medical and economic reasons for the shift to staples and clips from sutures and ligatures.
The first surgical staples to be used, and still the majority being used, were metal staples. But metal staples, when used externally, must be removed, with accompanying patient discomfort. And when metal staples are used internally, they are left in place. While the metal staples are tiny and become encapsulated by natural processes, and (except in a few cases, some of which will be discussed below) little or no difficulty has been associated with such staples left in the patient, for internal applications surgeons would prefer to use absorbable materials that eventually disappear after their usefulness has ended. For this reason, there is a substantial incentive to develop an absorbable plastic surgical staple.
It appears to be out of the question to produce an absorbable plastic surgical staple of reasonable size that fastens simply by bending back on itself in a manner analogous to the way metal staples fasten. The available absorbable plastics simply lack the required combination of ductility and stiffness that would be required for this purpose. For this reason, the initial attempts to produce an acceptable absorbable plastic surgical staple has concentrated on the staple/receiver type of fastener. In this type of fastener, a staple member includes a cross-piece or base and one or more attached legs which are designed to pierce the tissue to be fastened and to enter receptacles in the receiver on the other side of the tissue. The receiver holds the leg(s) tightly, with the tissue being held between the cross-piece or base and the receiving member. The desirable characteristics of such a fastener are the following:
(1) adequate stiffness in the legs to pierce the tissue without being deflected in such a way that they fail to meet the receptacles in the receiver; PA1 (2) adequate strength in the receiver to hold the legs; PA1 (3) strength retention in vivo for a period which may vary from about three to six weeks, depending on the function of the fastener; PA1 (4) dimensional stability at moderately elevated temperatures, e.g., up to 65.degree. C., so that the fastener will not warp when exposed to such temperatures, which are commonly encountered during shipping or storage in warm weather; PA1 (5) sterilizability; and PA1 (6) ability to be totally absorbed or at least non-palpable within a reasonable period of time. PA1 (a) a staple member including a base member and at least one pointed leg member extending substantially perpendicularly from said base member; and PA1 (b) a receiving member including an aperture arranged and constructed to receive and retain the free end of said leg member,
It has not proven to be an easy matter to obtain the requisite combination of properties. For instance, early designs of absorbable surgical staples utilized temporary metal reinforcement for the fastener legs during insertion of the staple to insure adequate stiffness. For instance see Noiles, U.S. Pat. No. 4,060,089 and Green, U.S. Pat. No. 4,402,445. An absorbable clip and an absorbable staple (both of which have been used commercially) were made from an 80/20 lactide/glycolide (mol/mol) copolymer. These fasteners have the disadvantage that they are dimensionally unstable when heated to temperatures over 120.degree. F. (49.degree. C.). Therefore, care must be taken in handling these fasteners, because temperatures well over 120.degree. F. are commonly encountered in shipping and storage in the U.S. during the warmer months.
Later commercial surgical staples are made from either of two blends of lactide and glycolide polymers such that in each case the blend has much greater than 50 percent lactide-based moieties. Specifically, one blend had an overall lactide/glycolide ratio of 71/29, by weight, and the other, 64/36, by weight. These staples (as well as the fasteners mentioned in the previous paragraph) persist for rather a long time in vivo because of their high lactide content. Also, for a long time before these staples disappear from the body, they are hard, palpable, and brittle. When they fail, it is by brittle failure such that hard fragments are formed; such fragments have a potential for causing discomfort or even tissue damage.
Absorbable ligating clips made from poly(p-dioxanone) have recently been introduced commercially. Metallic ligating clips have been used for some time.
In one type of surgery, some problems have been found with the use of metal surgical staples. A report entitled "Unusual Complications Following Abdominal Hysterectomy: Dyspareunia and Consort Glans Laceration After Vaginal Cuff Stapling", which appeared in the Journal of the Maine Medical Association, Vol. 71, June 1980, pages 169-170, related the following:
A line of metal surgical staples had been used to seal off the vaginal cuff during an abdominal hysterectomy. The patient complained of leukorrhea, dyspareunia, and post coital bleeding after the operation. Slight injury to her consort was also reported. The problem was found to be caused by the surgical staples that had been used during the hysterectomy. After removal of the staples (some of them had to be removed surgically), the problems disappeared.
Beresford has reported similar experiences with metallic staples used to seal the vaginal cuff during abdominal hysterectomy. (Ref.--"Automatic Stapling Techniques in Abdominal Hysterectomy", Surgical Clinics of North America, Vol. 64, No. 3, June 1984, pages 609-618.) For this reason, the use of absorbable staples in this type of operation would be highly desirable. Beresford (op. cited, supra) and McTammany ("Vaginal Cuff Closure During Abdominal Hysterectomy Using Absorbable Staples:, The Berks County Medical Record, Volume 77, February 1986, pages 35-36) have reported the use of absorbable staples in this procedure. It is believed that the staples used were the high lactide content staples discussed above. No traumatic problems of the type encountered with metallic staples have been reported with the use of these absorbable staples. However, Beresford reported that the line of absorbable staples can be palpated in the vaginal vault until they absorb. The time to complete absorption is reported to be of the order of 180 days. He also reported that some staple shedding occurred and that the staples appeared in the vaginal vault in some patients after 2 to 4 weeks. McTammany reported that in most of his patients in which the absorbable staples were used, white fragments of the row of staples could be seen after 4 to 6 weeks, and that the fragments crumbled when grasped by forceps.
This invention provides an absorbable surgical fastener, such as a surgical staple, a ligating clip, an anastomotic coupler, a fascia closure, or the like, that has an overall composition containing more than 50 percent of polymerized glycolide, and provides, unexpectedly, a highly desirable combination of properties. With such a high glycolide content, one would have expected the subject devices to have limited strength retention in vivo, since molded polyglycolide (homopolymer and high glycolide content copolymer) staples have an unacceptable strength retention profile in that they lose their strength in too short a period of time for most surgical uses. (Coworkers of the inventors herein have discovered that highly oriented, crystalline polyglycolide surgical devices made from extruded rods or filaments which have been shaped and then annealed while under restraint so as to prevent shrinkage, have significantly longer strength retention in vivo then molded devices made from the same polyglycolide polymers. However, the process for producing such devices is much more involved and expensive than simple molding. See U.S. Pat. No. 4,671,280 for a description of such highly oriented, crystalline devices.) However, the staples and other devices of this invention do retain a substantial proportion of their initial strength during the critical wound healing period, and only a short time (a few weeks) after the fasteners of the invention have served their purpose, they rapidly soften so that they become impalpable within about six to ten weeks after implantation.